1. Field of the Invention
The invention relates generally to a sootblower for removing debris from an interior of a boiler. More specifically, the invention relates to a sootblower that emits a pressure wave into an interior volume of the boiler to remove debris from surfaces located therewithin.
2. Related Technology
During the operation of large-scale combustion devices, such as boilers that burn fossil fuels, slag and ash encrustations develop on interior surfaces of the boiler. For example, boiler tubes that are grouped together as a tube bank and that each extend generally vertically within the boiler interior volume are particularly susceptible to the above-described deposits. The presence of these deposits degrades the thermal efficiency of the boiler. Therefore, it is periodically necessary to remove such encrustations. Various systems are currently used to remove these encrustations.
One such type of system includes a device referred to as a sootblower. Conventional sootblowers project a stream of cleaning fluid, such as air, steam or water, into the interior volume of the boiler. In the case of retracting type sootblowers, a lance tube is periodically advanced into and withdrawn from the boiler and conducts the cleaning fluid to spray from one or more nozzles fastened to the lance tube. As the lance tube is advanced into and withdrawn from the boiler, it may rotate or oscillate in order to direct one or more jets of cleaning fluid at desired surfaces within the boiler. In the case of stationary sootblowers, the lance tube is always maintained within the boiler.
Conventional sootblowers deliver the cleaning fluid, typically steam, into the boiler at a relatively high pressure to facilitate the removal of the encrustations. The high pressure steam typically must be heated and/or pressurized before entering the sootblower, thereby consuming energy and lowering the overall efficiency of the boiler system. In addition, conventional sootblowers depend on direct impact of the fluid stream with the boiler tubes to remove the deposits. As a result, the boiler tubes are often only cleaned on the leading side (the side directly impacted by the fluid stream). Furthermore, the jet penetration may be impeded by an obstruction, such as another boiler tube.
Systems that harness the power of chemically-driven combustion events, such as detonation and deflagration, are beneficial for boiler cleaning because they may have an improved efficiency. More specifically, the combustion events generate pressure waves, which are directed into the boiler interior volume to vibrate the interior components of the boiler and loosen debris therefrom. Additionally, the pressure waves may be more effective tubes than conventional sootblowers at removing deposits from the boiler tubes because the pressure waves are able to reverberate within the deposits. The reverberation is able to travel into the deposit and to wrap around the boiler tubes to effectively loosen the deposits from both the leading side and the trailing side of the boiler tubes.
A shock tube is a tube having an open end and a closed end that is used to generate the detonation or deflagration event. An explosive gas mixture is ignited at the closed end of the shock tube and a deflagration combustion wave is formed and accelerated to the point where transition from deflagration to detonation occurs. The detonation event produces a sharp shock wave having a peak pressure that may be several times greater than a reference pressure, depending primarily on the fuel and oxidizer that are utilized in the shock tube.
Detonation combustion differs from deflagration combustion in that during a detonation event a fuel/oxidizer mixture is detonated rather than burned. Detonation combustion leads to a much greater release of energy than deflagration, thereby creating greater pressures, higher temperatures, and much greater pressure wave velocities. Thus, while the pressure wave velocity due to a deflagration process is typically less than 0.03 times the speed of sound and typically develops a relatively low pressure, the pressure wave or shock wave velocity associated with detonation combustion typically approaches 5 to 10 times the speed of sound and offers pressure differentials of approximately 13 to 55 times greater than the reference pressure.
Stationary detonation or deflagration cleaners include a long, stationary tube positioned outside the boiler walls. The stationary tube is positioned in the opening such that a tube outlet that emits a pressure wave towards the boiler tubes does not extend into the interior volume. Alternatively, the tube slightly extends through the opening such that only a relatively small length of the tube extends into the boiler interior volume. In both of these cases, however, the tube outlet is positioned a relatively large distance from the boiler tubes, thereby reducing the cleaning effectiveness of the pressure wave. More specifically, the pressure wave typically decays in an exponential fashion after exiting the stationary tube. For example, the pressure wave may be able to effectively clean the first row of boiler tubes but not the rows located further away from the stationary tube outlet. Therefore, given the distance between the outlet of pressure wave generator and the boiler tubes, and given the obstruction represented by the banks of boiler tubes, cleaning by a stationary detonation tube may be limited. Furthermore, even if the sootblower is able to produce extremely high pressure waves that maintain enough strength to clean the back rows of boiler tubes, the front rows of boiler tubes may be damaged by the pressure waves, especially those associated with detonation combustion. The stationary detonation/deflagration lance tubes may have an especially limited cleaning effect on tenacious ash deposits.
In another cleaning system currently known in the art, disclosed in U.S. Pat. No. 5,494,004 entitled “ON LINE PULSED DETONATION/DEFLAGRATION SOOT BLOWER”, a cleaning apparatus is able to be moved through an inlet opening formed in a boiler wall. The cleaning apparatus includes a pair of elongated housing members that are pivotable with respect to each other to move between a folded position and a partially extended position. More specifically, when the housing members are in the folded position, the cleaning apparatus is able to be extended through the boiler wall inlet. Once inside the boiler, the pivoting housing member is pivoted to an angle Ø (FIG. 3) generally equal to 45 degrees so that pressure waves are able to be directed into the boiler. More specifically, the downstream end of the pivotable housing member includes a deflagration/detonation combustor for generating and emitting pressure waves into the boiler. However the weight of the portion of the sootblower that is extended into the boiler is greatly increased by locating the combustor within the pivotable housing member and thereby extending the combustor into the boiler. Therefore, due to structural limitations on the housing members, the sootblower is unable to be extended a substantial distance into the boiler. Additionally, because the deflagration combustor is located at the end of the pivotable housing member, the sootblower has a relatively small run-up distance, which will be discussed in more detail below. Furthermore, the pivotable-housing sootblower is unable to emit pressure waves into the boiler while traversing therein because the device cannot fit through the boiler wall opening when the housing members are partially extended and cannot emit pressure waves in a desired direction when the housing members are folded.
During operation of currently known, combustion-event cleaners, the pressure wave may fail to occur or may be undesirably weak due to various factors. For instance, if the mixture of the fuel and the oxidizer is not proper, then detonation or deflagration may not occur. If the pressure wave is not effective, the boiler tubes may experience undesirable deposit build-ups, which could reduce boiler efficiency or cause boiler shutdown. Although some currently-known combustion-event cleaners include a detonation/deflagration detection system, this system operates by measuring pressure waves generated by the cleaner, which may be difficult. More specifically, the pressure waves generated by the cleaner are in the range of microseconds and a direct data sampling is therefore not feasible.
It is therefore desirous to provide a combustion-event sootblower that is able to effectively loosen deposits from surfaces within a boiler and that is able to effectively detect unsuccessful detonation or deflagration.